1. Field of the Invention
The present invention relates to a hand shake blur detecting apparatus.
2. Description of the Related Art
A still image hand shake blur correction technique is a technique for reducing hand shake blur in photography (still image shooting), and is achieved by detecting the hand shake blur and stabilizing the image based on the detected result.
A method of detecting the hand shake blur includes a method of using a hand shake blur sensor (angular velocity sensor), and an electronic method of detecting by analyzing the image. The method of stabilizing the image may be an optical method in which the lens and imaging sensors are stabilized, or an electronic method in which the blur caused by hand shake is removed through image processing.
The completely electronic hand shake blur correction technique, that is, a technique of generating the image in which hand shake blur is removed by analyzing and processing only one photographed hand shake blur image has not reached the practical level. In particular, obtaining a hand shake blur signal of a precision obtained by a hand shake blur sensor is difficult by analyzing one hand shake blur image.
Therefore, it is realistic to detect the hand shake blur using the hand shake blur sensor, and remove the hand shake blur through image processing using the hand shake blur data. The removal of blur through image processing is referred to as image restoration. The method including the hand shake blur sensor and image restoration is herein referred to as an electronic hand shake blur correction.
Conventionally, an angular velocity sensor or an acceleration sensor is used as a device for detecting the hand shake blur of a video camera, a digital still camera and the like. The hand shake blur detecting apparatus thereof is also becoming miniaturized to miniaturize the equipment. However, when the detecting section of the hand shake blur detecting apparatus is miniaturized, the drift or offset component is added to the output signal due to change in temperature of the environment or rise in temperature caused by the use of the element itself, and the output precision lowers. In particular, that in which the detecting section is configured with a piezoelectric element is proposed to achieve miniaturization, but a large drift occurs at the output signal due to the change in electrostatic capacity in addition to the change in shape by change in temperature.
The technique for removing the drift component is proposed by Japanese Laid-Open Patent Publication No. 60-143330. This technique effectively removes only the drift component having low frequency compared to the hand shake blur component by applying a high pass filter (HPF) to the output signal of the angular velocity sensor. However, if the cut-off frequency of HPF is increased, the hand shake blur component is also removed. Further, if the cut-off frequency of the HPF is reduced, the time constant becomes large, and a long stable period becomes necessary to clear the residual component of the hand shake blur, and thus the stop state over a long period of time is necessary before shooting.
A countermeasure for the problem originating from the cut-off frequency of the HPF is proposed in Japanese Laid-Open Patent Publication No. 63-50729, Japanese Laid-Open Patent Publication No. 7-301836, Japanese Laid-Open Patent Publication No. 4-68322, and Japanese Laid-Open Patent Publication No. 7-20521.
In Japanese Laid-Open Patent Publication No. 63-50729, a technique of shortening the convergence time of the residual component of the hand shake blur by arranging a plurality of HPFs having different time constant, and switching from the HPF having a small time constant to the HPF having a large time constant is proposed. However, the offset component (DC component) becomes included in time of switching the HPF in this technique.
In Japanese Laid-Open Patent Publication No.7-301836, a technique of shortening the time for clearing the large hand shake blur residual component by changing the time constant of the HPF according to the size of the hand shake blur signal is proposed. However, the offset component (DC component) that is difficult to measure is included when changing the time constant of the HPF.
In Japanese Laid-Open Patent Publication No. 4-68322, a technique of giving a warning or prohibiting release until the output of the sensor stabilizes is proposed, but the photo opportunity may be missed.
In Japanese Laid-Open Patent Publication No. 7-20521, a technique of clearing the residual component in a moment without containing the offset component by initializing the HPF when the input signal of the HPF is 0 is proposed. However, in this technique, the residual component cannot be removed if the input signal of the HPF does not become 0 after the generation of large residual component.